1. Field of the Invention
The invention relates to a radial blower, in particular, for a breathing apparatus, comprising a blower housing with a central, axial intake opening and a radial or approximately tangential outlet opening as well as a motor-driven radial blower wheel arranged axially between the intake opening and the outlet opening and having a central inflow area neighboring the intake opening, wherein, in particular, the intake opening has arranged upstream thereof an intake spiral (xe2x80x9cintake air snailxe2x80x9d) at the exterior housing side such that a medium flows radially or approximately tangentially into a spiral channel and flows from there axially into the central intake opening.
2. Description of the Related Art
DE 197 15 581 C1 and the parallel EP 0 872 643 A2 describe an air supply arrangement for blowers of breathing apparatus, for example, for the treatment of sleep apnea, wherein, with interposition of the blower, an air supply channel is connected to an air outlet. In this connection, the intake spiral is provided for reducing noises generated by the air flow. The known intake spiral is characterized in that the spirally shaped air supply channel is divided into at least two partial channels. The thus resulting partial channels end directly in the vicinity of the central intake opening so that the incoming air reaches directly, i.e., substantially radially, the intake area of the blower wheel and impacts in this area on the inner ends of the blower wheel vanes. The air flows then through the blower wheel radially outwardly and subsequently axially in the direction of the outlet opening.
The present invention has the object to still further reduce the noise emission for such a radial blower.
The first solution according to the invention resides in that the radial blower wheel has at its axial side facing the outlet opening a cover disk with such a large diameter that between the outer circumference of the cover disk and an inner circumferential surface of the housing a constricted annular flow gap is formed for the medium flowing first radially through the radial blower wheel and then axially in the direction of the outlet opening. In this connection, it is particularly advantageous when the flow gap has an annular flow cross-section which is within a range from smaller than up to maximally 60% greater than the flow cross-section of the outlet opening.
It was found that with this feature according to the invention a distinct noise reduction is obtained. As a result of the constricted flow gap, a calming chamber is formed that encloses the blower wheel and is shaped as an annular chamber in which the medium flowing radially out of the blower wheel is first calmed and then guided via the constricted flow gap in the direction of the outflow chamber provided with the outlet opening and also shaped as an annular chamber.
A second solution according to the invention concerns the area of the intake spiral and resides in that the spiral channel is limited by a corresponding spirally shaped channel wall which, in the vicinity of the central intake opening, ends such that any imaginary tangent placed on the channel wallxe2x80x94in particular, also on its inner endxe2x80x94is positioned outside of the intake opening and the intake area of the blower wheel, or is positioned at most tangentially thereto. In this connection, the intake area of the blower wheel is formed by the radially inwardly positioned ends of the radial vanes wherein these inner ends of the radial vanes are positioned on a circle whose diameter is at least identical to, preferably however slightly greater than, the diameter of the intake opening.
This measure according to the invention is based on the recognition that by providing a lateral air supply according to the prior art (necessary because of the required very flat configuration) results in audible noises because the air flow coming from the intake spiral and entering the central intake area impacts directly approximately radially on the inner ends of the radial vanes and thus causes distinct noises. This can be described as the air flow xe2x80x9csees the inner ends of the vanesxe2x80x9d. According to the invention, the spiral channel is instead configured such that the air flow will lay itself substantially tangentially against the central opening toward the blower wheel so that the air flow does not impact directly on the radial vanes but instead has a soft transition. This means that the air, coming from the intake spiral, practically xe2x80x9csneaksxe2x80x9d noiselessly tangentially into the central intake opening and into the intake area.
The two measures according to the invention can be employed, as desired, alternatively, but with special advantage in combination with one another so that in a concrete realization of the invention a noise level was obtained which was approximately 13 dBA lower in comparison to a known blower, wherein this improvement is distributed possibly approximately half and half onto the two noise reduction measures according to the invention.
It should be noted that the measures according to the invention are suitable primarily for blowers with a relatively high pressure increase and small volume flow because for this configuration they provide the best sound reduction effect. For this purpose, a working point is selected on the blower characteristic line where for the rated volume flow a relatively small volume flow and a relatively high pressure are present. The rated volume flow and a free blowing volume flow then have a ratio of approximately 1:12 to 1:6, corresponding to approximately 8 to 16%. In an advantageous embodiment, the rated volume flow can be, for example, 50 l/min and the free-blowing volume flow can be 400 l/min resulting in a ratio of 1:8, corresponding to 12.5%.